This invention relates to combustion chambers for use in spark ignition engines having direct-injection fuel systems.
Spark-ignition, direct-injection combustion systems for internal combustion engines have been proposed to improve fuel economy when compared with more typical port fuel-injected combustion systems. The spark-ignition, direct-injection engine is provided with a high pressure fuel injection system that sprays fuel directly into the engine combustion chamber which is formed, at least partially, in the piston. The fuel is directed or transported to a specific region within the combustion chamber. This creates a stratified charge in the combustion chamber resulting in fuel economy benefits, since the throttling requirements are less restrictive and the fuel combustion characteristics are improved. Conventional fuel injectors providing a conical fuel spray may be used in such engines. However, injectors providing a fan shaped fuel spray have also been proposed.
U.S. patent application Ser. No. 09/930,707 filed Aug. 13, 2001 and assigned to the assignee of the present invention, discloses an improved combustion chamber for a spark ignition direct injection engine. The piston includes an oblong or oval shaped bowl, forming 50% to 70% of the total combustion chamber volume at piston top center, into which a fuel spray is injected during the piston compression stroke. Various physical and dimensional features of the piston and combustion chamber and the use of a conventional direct injection fuel injector are disclosed.
The present invention provides improved combustion chambers including fuel injectors having an oval fuel spray for use with direct injection engine combustion chambers of the type disclosed in the previously mentioned patent application U.S. Ser. No. 09/930,707 as well as in other applications.
In a preferred embodiment, a fuel injector is mounted on a side of the combustion chamber and delivers an ovalized fuel spray toward an oblong piston bowl of the associated combustion chamber. The ovality of the spray is selected in relation to the oblong piston bowl and the motion of the combustion chamber air charge during the piston compression stroke to maintain the fuel charge within the piston bowl volume (including the space above the bowl) during compression and combustion of the fuel charge in the chamber.
The shape of the oval spray may be adjusted as desired in relation to the shape of the piston bowl, as well as for use in other applications of an oval spray injector. As used in a specific embodiment the ovality of the fuel spray indicated by the ratio of the major axis to the minor axis is in the range of about 2/1 to 4/1 for delivery into an oblong piston bowl with an ovality of about 1.2/1 to 1.5/1.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.